The invention relates to checking and measuring trueness of a cylindrical bore, and more particularly to a method and apparatus for determining and measuring non-straightness of an elongated cylindrical bore utilizing a collimated light beam.
A capillary tube is an important element in a laser, and the capillary inspection step in the manufacturing process is vital to maximizing the optical output properties of a laser. Inspection methods prior to the present invention have utilized both mechanical and optical techniques in an effort to determine straightness of the capillary bore.
In mechanical testing, typically a rod of diameter slightly less than the nominal bore diameter was passed through the bore to check straightness. If the rod passed freely through the bore, this would verify bore straightness. If the rod failed to pass through, rods of slightly smaller diameter were attempted until one was found that would pass through bore, indicating the degree of non-straightness of the bore. This mechanical method required very clean conditions and provided only qualified
Prior optical testing methods for checking bore straightness have included (a) placing the capillary bore in the path of an external-mirror laser; and (b) visual observation of the inside of the capillary bore, with the naked eye or with the help of a lens. Placing the capillary in the active path of an external-mirror laser would in principle allow the optical properties of the beam path introduced by the test capillary to be measured. However, in practical effect, this prior method has been found to be of questionable resolve and has been difficult to implement.
Visual observation has been a common method for observation of capillary bore straightness. The visual method has utilized the multiple reflections of an illuminated end of a bore as the bore was observed from the opposite end. The reflections would produce rings down the bore length and the concentricity of the rings would give a relative measure of the bore straightness.
In other elongated bores, from very small to large diameters, including bores of rifles, for example, verification of straightness is required. Verification of other properties, such as diameter and trueness of bore position within a cylindrical body (eccentricity) is also required in many circumstances.
There has been a need, in the laser industry and in other fields, for a more precise and better quantified manner of inspection of bores. It is desirable to have a single method with the ability to inspect both straight cylindrical and tapered bore shapes, as well as to inspect capillaries of various lengths.